Method for the recovery of uranium from pregnant liquor solutions

ABSTRACT

A method for the recovery of uranium from pregnant liquor solutions that comprise levels of chloride of 5 to 80 g/L by using an amino phosphonic functionalized resin. The method includes providing an amino phosphonic functionalized resin; providing a pregnant liquor solution comprising and uranium; passining the pregnant liquor solution over the amino phosphonic functionalized resin to separate the uranium from the pregnant liquor solution; and eluting the uranium.

The present invention is directed to a new more environmentally friendlymethod for the recovery of uranium from acid leach pregnant liquorsolutions that comprise high levels of chloride by using an aminophosphonic functionalized resin.

Numerous minerals are present in subsurface earth formations in verysmall quantities which make their recovery extremely difficult. However,in most instances, these minerals are also extremely valuable, therebyjustifying efforts to recover the same. An example of one such mineralis uranium. However, numerous other valuable minerals, such as copper,nickel, molybdenum, rhenium, silver, selenium, vanadium, thorium, gold,rare earth metals, etc., are also present in small quantities in somesubsurface formations, alone and quite often associated with uranium.Consequently, the recovery of such minerals is fraught with essentiallythe same problems as the recovery of uranium and, in general, the sametechniques for recovering uranium can also be utilized to recover suchother mineral values, whether associated with uranium or occurringalone. Therefore, a discussion of the recovery of uranium will beappropriate for all such minerals.

Uranium occurs in a wide variety of subterranean strata such as granitesand granitic deposits, pegmatites and pegmatite dikes and veins, andsedimentary strata such as sandstones, unconsolidated sands, limestones,etc. However, very few subterranean deposits have a high concentrationof uranium. For example, most uranium-containing deposits contain fromabout 0.01 to 1 weight percent uranium, expressed as U₃O₈ as isconventional practice in the art. Few ores contain more than about 1percent uranium and deposits containing below about 0.1 percent uraniumare considered so poor as to be currently uneconomical to recover unlessother mineral values, such as vanadium, gold and the like, can besimultaneously recovered.

There are several known techniques for extracting uranium values fromuranium-containing materials. One common technique is roasting of theore, usually in the presence of a combustion supporting gas, such as airor oxygen, and recovering the uranium from the resultant ash. However,the present invention is directed to the extraction of uranium values bythe utilization of aqueous leaching solutions. There are two commonleaching techniques (or lixiviation techniques) for recovering uraniumvalues, which depend primarily upon the accessibility and size of thesubterranean deposit. To the extent that the deposit containing theuranium is accessible by conventional mining means and is of sufficientsize to economically justify conventional mining, the ore is mined,ground to increase the contact area between the uranium values in theore and the leach solution, usually less than about 14 mesh but in Somecases, such as limestones, to nominally less than 325 mesh, andcontacted with an aqueous leach solution for a time sufficient to obtainmaximum extraction of the uranium values. On the other hand, where theuranium-containing deposit is inaccessible or is too small to justifyconventional mining, the aqueous leach solution is injected into thesubsurface formation through at least one injection well penetrating thedeposit, maintained in contact with the uranium-containing deposit for atime sufficient to extract the uranium values and the leach solutioncontaining the uranium, usually referred to as a “pregnant” liquorsolution (PLS), is produced through at least one production wellpenetrating the deposit. It is this latter in-situ leaching ofsubsurface formations to which the present invention is directed.

The most common aqueous leach solutions are either aqueous acidicsolutions, such as sulfuric acid solutions, or aqueous alkalinesolutions, such as sodium carbonate and/or bicarbonate.

Aqueous acidic solutions are normally quite effective in the extractionof uranium values. However, aqueous acidic solutions generally cannot beutilized to extract uranium values from ore or in-situ from depositscontaining high concentrations of acid-consuming gentle, such aslimestone. While some uranium in its hexavalent state is present in oresand subterranean deposits, the vast majority of the uranium is presentin its valence states lower than the hexavalent state. For example,uranium minerals are generally present m the form of uraninite, anatural oxide of uranium in a variety of forms such as UO₂, UO₃, UO.U₂O₃and mixed U₃O₈(UO₂.2UO₃), the most prevalent variety of which ispitchblende containing about 55 to 75 percent of uranium as UO₂ and upto about 30 percent uranium as UO₃. Other forms in which uraniumminerals are found include coffinite, carnotite, a hydrated vanadate ofuranium and potassium having the formula K₂(UO₂)₂(VO₄)₂.3H₂O, anduranites which are mineral phosphates of uranium with copper or calcium,for example, uranite lime having the general formula CaO.2UO₃.P₂O₅.8H₂O.Consequently, in order to extract uranium values from subsurfaceformations with aqueous acidic leach solutions, it is necessary tooxidize the lower valence states of uranium to the soluble, hexavalentslate.

Combinations of acids and oxidants which have been suggested by theprior art include nitric acid, hydrochloric acid or sulfuric acid,particularly sulfuric acid, in combination with air, oxygen, sodiumchlorate, potassium permangante, hydrogen peroxide and magnesiumperchlorate and dioxide, as oxidants. However, the present invention isdirected to the use of sulfuric acid leach solutions containingappropriate oxidants and other additives, such as catalysts.

There are two commonly used methods for the recovery of uranium frompregnant liquor solution (PLS). One technique, solvent extraction,employs the use of a non aqueous solvent to selectively extract uraniumfrom the PLS.

The second method involves ion exchange technology. Strong and weak baseanion exchange resins are commonly used. This ion exchange method hasbecome the more preferred method of uranium recovery in various regionsof the world because of its environmental benefits as well as its safetybenefits. Flammable toxic solvents need not be used for the presentmethod as compared to the solvent extraction method where harmfulchemicals are employed.

Additionally it has been discovered that in environments where there isa relatively high concentration of chloride, i.e. greater than 5 g/L,based on the composition of the PLS fouling of the ion exchange resinoccurs. This fouling results in a decreased loading capacity of theresin. U.S. Pat. No. 4,599,221 uses an amino phosphonic functionalizedresin to recover uranium from phosphoric acid; however a need exists fora method to recover uranium from acid leach in high chlorideenvironments. Recovery of uranium from phosphoric acid is a differentprocess from the acid leach process because there are competing ions,such as chloride, in and acid leach solution that can foul any recoverymedia. The phosphoric acid process does not have such. Additionally, thelevels of uranium in a phosphoric acid process are relatively low, i.e.less than 300 ppm. In acid leach, the batting capacity of uranium mustbe much greater as the levels of uranium in acid leach liquors can bepresent in up to 2000 mg/L (or ppm) It is known that for the sameconcentration of U in the PLS, the operating capacity is much greater inacid leach liquor than in phosphoric acid liquor. Therefore one of skillin the an would not typically apply the same techniques from therecovery of metals from phosphoric acid to acid leach.

The present invention solves these problems of the art by proving anamino phosphonic functionalized resin useful for the recovery of uraniumthat does not foul in chloride environments of greater than 5 g/L.

The present invention provides a method for the recovery of uranium froma pregnant liquor solution comprising:

i) providing an amino phosphonic functionalized resin;

ii) providing a pregnant liquor solution comprising chloride anduranium;

iii) passing the pregnant liquor solution over the amino phosphonicfunctionalized resin to separate the uranium from the pregnant liquorsolution; and

iv) eluting the uranium

wherein the chloride is present in an amount from 5 to 80 g/L.

FIG. 1 shows a graph of the results of dynamic loading versus flow ratein the Example; and

FIG. 2 shows a graph of the results of uranium concentration versus pHin the Example.

As used herein the term amino phosphonic functionalized resin is meantto include either an amino phosphonic resin or an amino hydrophosphonicfunctionalized resins.

In the present invention the resin is a styrene polymer resin havingactive amino phosphonic functional groups linked to the polymer matrix.The term “styrene polymer” indicates a copolymer polymerized from avinyl monomer or mixture of vinyl monomers containing styrene monomerand/or at least one crosslinker, wherein the combined weight of styreneand cross linkers is at least 50 weight percent of the total monomerweight. The level of cross linking ranges from 4 to 10%. All percentagesherein are weight percentages.

A crosslinker is a monomer containing at least two polymerizablecarbon-carbon double bonds, including, e.g., divinylaromatic compounds,di- and tri-(meth)acrylate compounds and divinyl ether compounds.Preferably, the crosslinker(s) is a divinylaromatic crosslinker, e.g.,divinylbenzene.

The structure of the polymer can be either gel or macroporous(macroreticular). The term “gel” or “gellular” resin applies to a resinwhich was synthesized from a very low porosity (0 to 0.1 cm³/g), smallaverage pore size (0 to 17 Å) and low B.E.T. surface area (0 to 10 m²/g)copolymer. The term “macroreticular” (or MR) resin is applied to a resinwhich is synthesized from a high mesoporous copolymer with highersurface area than the gel resins. The total porosity of the MR resins isbetween 0.1 and 0.7 cm³/g, average pore size between 17 and 500 Å andB.E.T. surface area between 10 and 200 m²/g. The resin is in acid form.

The resin is used to treat an acid leach pregnant liquor solution (PLS).The PLS of the present invention comprises uranium and chloride. Uraniumis primarily present in the form of U₃O₈; although other commonly knownforms and isotopes of uranium may be present.

As used herein, the term uranium refers to all forms and isotopes ofuranium. Uranium is present in the PLS in an amount from 25 to 2000mg/L, preferably from 50 to 1500 mg/L, and further preferably from 100to 1000 mg/L. Chloride ion and chloride complexes together as “chloride”is present in the PLS in an amount from 5 to 80 g/L and preferably form7 to 70 g/L and further preferably from 15 to 50 g/L. The PLS of thepresent invention may optionally contain a variety of other components.Such components include but are not limited to: iron, sulfuric acid,sodium, calcium, potassium, copper, phosphorus, and aluminum. The pH ofthe PLS is acidic and ranges from 0 to 4. Furthermore, the PLS may beobtained from any method commonly known to those of skill in the artincluding but not limited to in situ leach, heap, leach, resin in pulp,and in situ recovery.

Uranium is separated from the PLS by passing the PLS over the aminophosphonic functionalized resin. Techniques commonly used in the art toseparate the uranium from the PLS may be applied. Such techniquesinclude but are not limited to fixed bed, co-current or countercurrentfluidized bed. The process may be batch or continuous. Typically theflow rate within the column or packed bed system is from 0.5 to 50 BV/h,preferably 1 to 50 BV/h, more preferably 2 to 45 BV/h.

The amino phosphonic functionalized resin retains the uranium from thePLS and the uranium is then recovered by elution. Methods of elutionused by those of ordinary skill in the art are used herein. In oneinstance, for example, the uranium loaded resin may be treated with asolution of ammonia or ammonia hydroxide. Afterwards, the resin iseluted with a solution of sodium carbonate. The uranium is thenrecovered from solution by known separations techniques, such as forexample precipitation. It is beneficially found that the at least 10% ofthe uranium found in the original PLS may be recovered. Within the pHrange of 0 to 4 of the PLS, uranium recovery levels of up to 25% may beachieved.

EXAMPLES

Laboratory Equipment Used

Jacketed glass column (height 30 cm, Ø 2-3 cm, fitted with sinteredglass of porosity 1). Peristaltic pump with flexible tubings 10, 100graduated cylinder. 25 mL plastic flasks for samples collections.Stopwatch. Appropriate equipment for Uranium analysis (I.e: ICP).Standard laboratory glassware

Resin Used

AMBERLITE™ IRC 747, is a registered trademark of Rohm and Haas Company,a wholly owned subsidiary of The Dow Chemical Company. The resin is insodium form having a polystyrenic matrix, crosslinked with divinylbenzene and containing aminophosphonic functional groups.

Note

The resin was converted in its appropriate ionic form (i.e: acidic form)before carrying out the experiments.

Example

Experiment 1: A solution containing 200 mg/L of uranium (expressed asU), 24 g/L of sulfate, 0 g/L of chloride 2 g/L of iron (as Fe³⁺) waspassed through AMBERLITE IRC 747 at 5 BV/h.

Experiment 2: A solution containing 200 mg/L of uranium (expressed asU), 24 g/L of sulfate, 20 g/L of chloride 2 g/L of iron (as Fe³⁺) waspassed through AMBERLITE IRC 747 at 5 BV/h.

Experiment 3: A solution containing 200 mg/L of uranium (expressed asU), 24 g/L of sulfate, 0 g/L of chloride 2 g/L of iron (as Fe³⁺) waspassed through AMBERLITE IRC 747 at 2.5 BV/h.

Experiment 4: A solution containing 200 mg/L of uranium (expressed asU), 24 g/L of sulfate, 20 g/L of chloride 2 g/L of iron (as Fe³⁺) waspassed through AMBERLITE IRC 747 at 2.5 BV/h.

All experiments were carried out at 25° C. A sample was taken every 10bed volumes for uranium analysis. The leakage curves were obtained asshown in FIG. 1.

FIG. 1 shows that the resin loading is not affected when the chlorideconcentration increases from 0 to 20 g/L.

The uranium loading increases when the flow rate decreases. Theoperating capacity is around 15 g/LR (expressed as U) at a flow rateequates to 5 BV/h and around 21 g/LR (expressed as U—g/LR stands for“gram per liter of resin in its ionic form considered”—i.e: acidic form)when the flow rate equates 2.5 BV/h.

Elution

The loaded resins were treated with 2 bed volumes of a solution ofammonia hydroxide at a concentration of 1 mol/L (1N). Afterwards, theresins were eluted with a solution of sodium carbonate at aconcentration of 1 N.

The totality of uranium loaded was eluted within 7 bed volumes of sodiumcarbonate solution.

Experiment 5: Several solutions containing 200 mg/L of uranium(expressed as U), 24 g/L of sulfate, 0 g/L of chloride were prepared.Each solution was adjusted a different pH level. A sample of resin wasput in contact with each solution. The ratio of 1 part resin to 50 partsof solution was kept constant in order to avoid any externalperturbation. After shaking for 8 hours, the analysis of the uraniumresidual in the supernatant was analyzed and the resin loadingdetermined. FIG. 2 indicates that the optimum loading is obtained whenthe pH equates 4. Above pH 4, precipitation of Uranium was observed. Itwas also observed that the loading was very good at pH 0. The resultsare shown in FIG. 2.

What is claimed is:
 1. A method for the recovery of uranium from apregnant liquor solution comprising: i) providing an amino phosphonicfunctionalized resin in acid form; ii) providing a pregnant liquorsolution comprising chloride and uranium; iii) passing the pregnantliquor solution over the amino phosphonic functionalized resin toseparate the uranium from the pregnant liquor solution; and iv) elutingthe uranium wherein the chloride is present in an amount from 5 to 80g/L, and wherine the pregnant liquor solution has a pH of from 0 to 4.2. The method of claim 1 wherein the pregnant liquor solution comprisesfrom 25 to 2000 mg/L uranium.
 3. The method of claim 1 wherein thepregnant liquor solution comprises from 7 to 70 g/L chloride.
 4. Themethod of claim 1 further wherein at least 10% of the amount of uraniumfrom the pregnant liquor solution is recovered.
 5. The method of claim 1further wherein up to 25% of the amount of uranium from the pregnantliquor solution is recovered.